feat(nightlight): scheduled blue-light filter via hyprsunset

Add nomarchy.nightlight (opt-in): a scheduled colour-temperature shift via
the HM services.hyprsunset module -- warm (.temperature, default 4000K) at
night, identity (no shift) by day, switching at .sunset / .sunrise. Two
time-based hyprsunset profiles, so hyprsunset handles the schedule and the
on-login state. New modules/home/nightlight.nix, imported in the home module.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/options.nix

@@ -157,6 +157,33 @@ in
       '';
     };
 
+    nightlight = {
+      enable = lib.mkEnableOption ''
+        a scheduled blue-light filter (hyprsunset): warm at night, no shift
+        by day. Opt-in; tune the temperature + sunrise/sunset below'';
+
+      temperature = lib.mkOption {
+        type = lib.types.int;
+        default = 4000;
+        example = 3500;
+        description = "Warm colour temperature (K) applied at night — lower is warmer.";
+      };
+
+      sunrise = lib.mkOption {
+        type = lib.types.str;
+        default = "07:00";
+        example = "06:30";
+        description = "Time (HH:MM) the filter turns OFF — daytime, no colour shift.";
+      };
+
+      sunset = lib.mkOption {
+        type = lib.types.str;
+        default = "20:00";
+        example = "21:00";
+        description = "Time (HH:MM) the filter turns ON — warm.";
+      };
+    };
+
     monitors = lib.mkOption {
       type = lib.types.listOf monitorType;
       default = [ ];